Wireless communication systems, such as the 3rd Generation (3G) of mobile telephone standards and technology, are well known. An example of such 3G standards and technology is the Universal Mobile Telecommunications System (UMTS), developed by the 3rd Generation Partnership Project (3GPP) (www.3gpp.org).
Typically, wireless communication units, or User Equipment (UE) as they are often referred to in 3G parlance, communicate with a Core Network (CN) of the 3G wireless communication system via a Radio Network Subsystem (RNS). A wireless communication system typically comprises a plurality of radio network subsystems, each radio network subsystem comprising one or more cells to which UEs may attach, and thereby connect to the network.
The 3rd generation of wireless communications has been developed for macro-cell mobile phone communications. Such macro cells utilise high power base stations (NodeBs in 3GPP parlance) to communicate with UEs within a relatively large coverage area.
Lower power (and therefore smaller coverage area) femto-cells or pico-cells are a recent development within the field of wireless cellular communication systems. Femto-cells or pico-cells (with the term femto-cells being used hereafter to encompass pico-cells or similar) are effectively communication coverage areas supported by low power base stations (otherwise referred to as Access Points (APs)). These cells are able to be piggy-backed onto the more widely used macro-cellular network and support communications to UEs in a restricted, for example ‘in-building’, environment. Typical applications for such femto-cell APs include, by way of example, residential and commercial (e.g. office) locations, ‘hotspots’, etc, whereby an AP can be connected to a core network via, for example, the Internet using a broadband connection or the like. In this manner, femto-cells can be provided in a simple, scalable deployment in specific in-building locations where, for example, network congestion at the macro-cell level may be problematic.
In a femto cell network it is known that there may be a very large number of femto cells compared to the number of macro cells, with femto cells often residing within or overlapping macro cells in the same geographic area.
Thus, the coverage area of a single macro cell will inevitably overlap (and encompass) a coverage area of a large number of femto cells.
In a planned macro cell network, a so-called neighbour cell list is used to identify adjacent cells to each macro cell, to facilitate handover of UE communications between cells. The neighbour cell list is broadcast to roaming UEs via NodeBs to enable the roaming UE to receive and assess the suitability of continuing a communication by transferring the communication to an adjacent (neighbour) cell. The neighbour cell list of the macro cell contains frequency and scrambling code information for all of the cells whose coverage area overlaps with the macro cell, to allow the UE to be able to receive and decode transmissions from the neighbouring cells.
In the same manner as for current macro cell systems, a downlink coverage area of a wideband code division multiple access (WCDMA) based femto cell is dependent on the power level of the Primary Common Pilot Channel (P-CPICH) relative to the surrounding interference level.
However, it is anticipated that femto cells will generally experience more diverse radio frequency (RF) environments, due to their anticipated in-building usage as well as their increased dependency upon factors such as distance to neighbouring macro cells/femto cells, thereby number of interfering neighbour cells, respective power levels of neighbouring macro/femto cells, floor-plan and materials used in the construction of the building in which the femto cell is located, etc.
The P-CPICH power setting in traditional macro cells is determined by centralized radio network planning, as illustrated in the flowchart 100 of FIG. 1, and as described in J. Laiho et. al., “Radio Network Planning and Optimisation for UMTS”, second edition, John Wiley & Sons, Ltd, ISBN-10 0-470-01575-6. This central pre-planning is often supplemented using techniques such as ‘drive-by’ testing. Referring now to FIG. 1, a flowchart 100 of a known process to set a P-CPICH power level in a 3GPP macro-cell network is illustrated.
In a macro cell network, the process comprises obtaining a set of network parameters, for example number of sites, terrain information, anticipated cell loads, quality of service (QoS) parameters, etc. as shown in step 105. Once the network parameters have been obtained in step 105, a potential cell site location is selected, as shown in step 110. The network parameters according to a cell site positioned in the selected location is then modelled to identify its radio network performance, as shown in step 115. The network model is then run a number of times to identify whether an optimal performance can be achieved with iterative changes to the network parameters or proposed cell site location, as shown in step 120.
If a suitably optimal performance is not achieved, for example the level of performance does not exceed a number of target thresholds, one or more network parameters are again modified, as shown in step 125, and the process loops back to step 110.
However, if a suitably optimal performance is achieved in step 120, a P-CPICH power level is set, as shown in step 130. Thereafter, network higher layer measurements may be taken and applied to the model as shown in step 135. Alternatively, or additionally, drive-by testing may be performed when the macro/micro system goes ‘live’, as shown in step 140. Measurements taken during the drive-by testing may then optionally also be applied to the Network model, as shown in step 145. In this manner, by supplementing the modelled nature of the macro/micro cell site with drive-by data, the Network Operator is able to check that the performance of the real-life system accurately reflects the modelled performance.
At present centralized radio network planning and techniques such as drive-by testing are utilized for the tuning of the P-CPICH power in the macro/micro cells, but will be unusable in a femto cell scenario. It is envisaged by the inventors of the present invention that some form of auto-provisioning of femto cells may be desirable from a Network Operator's perspective, especially in a large scale deployment of femto cells.
Thus, there exists a need for a wireless communication system, a network element and method for setting a power level in the wireless communication system, particularly in a system that combines macro-cell and femto-cells, which aims to address at least some of the shortcomings of past and present techniques.